Amanda Knox pauses while speaking during a news conference at Sea-Tac International Airport, Washington after landing there on a flight from Italy on Oct. 4, 2011. Italy's highest appeals court Knox's acquittal in the Meredith Kercher murder trial, on Tuesday, March 26, 2013.

ROME — Italy’s top court on Tuesday overturned the 2011 acquittal of American student Amanda Knox and her former boyfriend Raffaele Sollecito for the murder of Briton Meredith Kercher, and ordered a retrial.

The decision by the Court of Cassation is a new twist to a long-running case whose initial handling was sharply criticised by independent forensic experts.

Prosecutors accused Knox and Sollecito of killing Kercher in 2007 during a drug-fuelled sexual assault.

The two were initially found guilty and sentenced to 26 and 25 years in prison respectively after a trial that grabbed headlines all over the world.

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In 2011, their convictions were overturned after forensic investigators challenged police scientific evidence, saying there had been multiple errors in the investigation. Knox and Sollecito were released after serving four years in prison.

A third person, Ivorian Rudy Guede, was found guilty and sentenced to 16 years in a separate trial. He is now the only person serving time for the murder, although prosecutors say he could not have killed Kercher by himself.

Last year, prosecutors filed a motion to appeal against the acquittals, calling the verdicts “contradictory and illogical”.

Italy’s top appeal court made the ruling on Tuesday after examining whether there were procedural irregularities which gave grounds for a retrial, rather than assessing the details of the case. Its reasons will be announced later.

The new trial will be held before a court in Florence.

Kercher, a student at Leeds University, was 21 when she died.

Knox returned to her Seattle-area home after she was released from prison in Italy and had been scheduled to speak publicly about the trial for the first time on American television in April, when her book about the case is due to be released.